The invention relates to reduced energy content pigmented coating compositions, especially pigmented paints of low to medium sheen, also known as matt or soft sheen paints. In particular it relates to paints of pigment volume content from 78 to 85% and having sheen of less than 30% when measured at 85°.
Light colored pigmented paints usually contain high levels of titanium dioxide, TiO2. This is because such pastel shades are predominantly white with a small amount of non-white color added. Titanium dioxide is the best source of whiteness due to its high refractive index relative to typical binders used in paints. Unfortunately, TiO2 requires large amounts of energy to extract it from the ground and then purify. In fact, in known high pigment volume content (PVC) paints of pastel/light color, for example, matt whites and matt light shades as hereinbelow described, the high TiO2 content (typically 10 to 20 vol %) used to achieve the desired color and opacity is the main contributor to the total energy content of the paint.
By energy content, we mean the energy required to extract, refine and manufacture the ingredients comprising the paint; and the energy required to manufacture the paint itself.
Since most energy is generated by burning fossil fuel, high energy content usually results in high carbon dioxide emissions—hence the use of the alternative measure ‘embedded CO2’ to indicate the energy content.
The adverse effect of such emissions on the global environment, especially climate change, is generally accepted by most serious commentators. Thus, there is a need to reduce the energy consumed in producing such paints.
One approach to this is to reduce the TiO2 content of the paint. However, this simply reduces the opacity of the dried coating and, whilst each coat of dried paint may well have reduced energy content, additional coats will be required in order to achieve opacity. Consequently, any benefit is lost or at least, significantly diminished. Other approaches replace some or all of the TiO2 with extender pigments such as chalk. Whilst such extenders require less energy than TiO2 to extract and refine, the lower refractive index of such extenders is very close to the binders used in paint. As such, they do not scatter light as well as TiO2 and in order to compensate for the reduced amount of TiO2 more extender must be added to the paint to achieve the correct color and opacity. However, this raises the PVC further, eventually to the extent that air is trapped in the dried paint film. Whilst this increases the opacity, it also usually results in poorer wet scrub resistance.
One possible way out of this dilemma is to use calcined clay as this has good opacity and is less detrimental to the scrub resistance. However, manufacture of calcined clay requires clay to be heated to 1000° C. thereby consuming large amounts of energy. Clearly, this does not result in significant energy savings and is thus not a preferred option.
U.S. Pat. No. 4,277,385 discloses paint compositions having PVC between 75 and 85% and further teaches that to avoid cracking in high PVC paint films, the formulation should be free of non-opacifying inorganic pigments (another name for extenders) essentially replacing them with non-film forming solid polymer particles. However, no attempt is made to minimize the TiO2 content in these formulations and, thus the problem of high energy content and high CO2 emissions are not addressed.
European Patent application EP 0113435 describes an aqueous paint having reduced TiO2 content at PVC from 20 to 80%. It teaches to use mixtures comprising pigmented vesiculated polymer beads and larger opaque polymer particles having microvoids—but no pigments, to replace TiO2 whilst maintaining burnish/scrub resistance. However, as pointed out in that application, pigmented vesiculated polymer beads themselves contain TiO2 and thus add considerably to the TiO2 content. This does little, if anything, to reduce the total energy content of the paint. Pigmented vesiculated polymer beads are polymer particles containing both and TiO2 microvoids.
Thus, there is a need for improved paint compositions having reduced TiO2 content and thus low energy content whilst also having good opacity and good wet scrub resistance.